1. Field of the Invention
Aspects of the present invention relate to a thin film transistor, a method of manufacturing the same, and a flat panel display device including the same.
2. Description of the Related Art
A thin film transistor generally includes: an activation layer including a channel region, a source region, and a drain region; and a gate electrode which is formed on the channel region. The gate electrode is electrically insulated from the activation layer, by a gate insulating film.
An activation layer is generally formed of semiconductor material, such as amorphous silicon or poly-silicon. However, if an activation layer is formed of amorphous silicon, it is difficult to implement a high speed driving circuit, due to it having low electron mobility. If the activation layer is formed of poly-silicon, a separate compensation circuit should be added, due to uneven threshold voltages.
A conventional method of manufacturing a thin film transistor, using a low temperature poly-silicon (LTPS), involves an expensive process such as a laser annealing. In addition, such a method is difficult to apply to larger substrates.
Research into using a compound semiconductor as an activation layer has been recently conducted, in order to solve the above problems. For example, Japanese Patent Laid-Open Publication No. 2004-273614 discloses a thin film transistor that has a zinc oxide (ZnO), or a compound semiconductor having zinc oxide (ZnO), as a main ingredient, as an activation layer.
The compound semiconductor is evaluated as a stable material, having an amorphous shape. If such a compound semiconductor is used as an activation layer, the compound semiconductor has various advantages, in that the thin film transistor may be manufactured at a temperature below 350° C., using existing processing equipment. In addition, an ion implantation process may be omitted.
However, a compound semiconductor can be damaged by plasma, when a thin film formed thereon is etched. Such damage degrades the electrical properties of the compound semiconductor, such that the threshold voltage of the thin film transistor changes.